A powerful Nor’easter slammed the New York City region Thursday morning, delaying trains, disrupting air travel and making a slushy mess of the a.m. commute.

“Expect flight delays and cancellations to increase ahead of the winter storm as it moves northward along the coast,” meteorologist Alex Sosnowski said on AccuWeather.com.

As of 9 a.m., 5,402 flights had been grounded in the US, including 493 at LaGuardia, 328 at Kennedy and 620 at Newark airports, according to FlightAware.com and the Port Authority.

At LaGuardia, Mary Jane Fouse, 33, and her husband Pablo, 30, of Argentina had planned to catch a connecting flight to Chicago, but their 7 a.m. American Airlines flight had been cancelled.

They were on standby for a 6 p.m. flight and had already checked out of their hotel.

“If we don’t get on that flight, we have to sleep here,” said Mary Jane. “We don’t know anyone here. We have no where to stay so we are hoping for the best.”

“I’m disappointed and sad,” said Pablo. “We planned this for five months and were looking forward to it. I expected [their vacation] to be smooth and fun, not to be trapped by snow.”

They are still optimistic they will make it to their Chicago hotel by Thursday night.

Heavy snow mixed with freezing rain was falling and was expected to continue until early Friday, turning to all rain at times as temperatures rise through the day Thursday.

Forecasters said New York City can expect up to a foot of snow, with a foot or more predicted for areas north and west of the city.

And Gov. Cuomo tweeted out an announcement declaring a state of emergency.

“I am declaring a State of Emergency for the mid-Hudson, NYC and Long Island regions,” Cuomo tweeted, adding that people should stay home and off the roads so crews can plow and apply salt.

The declaration means that state resources, like snow plowing equipment, will be permitted to assist local cities, towns and villages with snow removal.

The declaration also allows the state to provide local municipalities with salt and other supplies to help with the effort.

New York City schools remained open, though field trips were cancelled due to dangerous travel conditions. Most suburban districts were closed.

The massive storm – which crippled parts of the South, leaving hundreds of thousands of people without electricity – could also cause some coastal flooding during high tide, which will be higher than usual because of Friday’s full moon.

“As the storm strengthens Thursday into Thursday night, enough onshore wind may be generated to cause minor flooding at times of high tide from New Jersey to Maine,” Sosnowski said.

The LIRR and PATH were reporting delays, and Metro-North established a modified schedule on the Harlem, Hudson and New Haven lines, cancelling or combining many trains.

Many subway lines were also delayed.

Amtrak also cancelled some trains and modified the schedules for others.

Acela Express trains between Washington and Boston, Northeast Regional trains between Boston and Norfolk, Va., Keystone Service between New York and Harrisburg, Pa., and Empire Service between New York and Albany, N.Y., are operating at reduced frequency or modified schedules Thursday. The Silver Meteor from New York to Miami was cancelled.

New York City has issued a snow alert, and the sanitation department said salt spreaders and plows were on the job in all five boroughs.

Major streets in Manhattan, such as Madison, Fifth and Sixth avenues in Midtown, remained covered in an inch or more of slush as of 7 a.m.

Alternate side of the street parking rules were suspended in the city on Thursday, though motorists still had to feed the meters.

Elsewhere, the situation was far worse.

Small armies of utility workers labored to turn the lights and heat back on for hundreds of thousands of Southerners after the storm left them powerless.

The Deep South remained a world of ice-laden trees and driveways early Thursday after several unusual days of sleet and snow brought by the powerful system.

At least 12 deaths across the South have been blamed on the stormy weather.

Drivers in and around Raleigh, N.C., became snarled Wednesday in huge traffic jams and abandoned cars in scenes reminiscent of motorist woes in Atlanta during a storm two weeks earlier.

In Atlanta, many streets were eerily quiet, with drivers heeding dire warnings to stay off the roads. State troopers say they worked more than 200 crashes in Georgia.

For some on slick, snow-covered interstates in North Carolina, commutes that should take minutes lasted hours after many got on the highways just as soon as snow and sleet began at midday.

And in South Carolina, more accustomed to occasional hurricanes, some could only relate the damage from ice-snapped tree limbs to that of bygone Hurricane Hugo.

Even normally balmy Myrtle Beach, where millions of visitors cavort each summer, cars were coated in thick ice that also frosted palm trees and kiddie rides by the shore.

“I hate driving on this,” grumbled South Carolina resident Mindy Taylor, 43, on her way for rock salt, kitty litter or anything else to melt the ice. “Hopefully it’ll warm up by the weekend and it will all melt. I’m ready for Spring.”

.Ice combined with wind gusts up to 30 mph snapped tree limbs and power lines.

About 350,000 homes and businesses lost electricity in Georgia, South Carolina had about 245,000 outages, and North Carolina around 100,000.

As he did for parts of Georgia, President Barack Obama declared a disaster in South Carolina, opening the way for federal aid.

Washington, D.C., could see around 8 inches of snow. Federal offices and both airports there were closed.